1. Field of the Invention
The present invention relates to a compressed air drive type dental handpiece which is light in weight and easy to handle.
2. Statement of the Prior Art
Generally, the dental handpiece designed to be driven by compressed air is broken down into two- and four-hole types which include respectively two and four fluid paths extending from a tube for fluid passage connected with the body of a dental unit to the head of a dental handpiece body. The fluids flowing through these paths in the case of the two-hole type are compressed air pressurized to 2 to 5 kg/cm.sup.2 and supplied for driving an air turbine that is a rotary member built in the head and cooling water pressurized to 1.5 to 2.5 kg/cm.sup.2 and sprayed from a nozzle of the head. In addition to the paths for the fluids used in the aforesaid two-hole type, the four-hole type includes those for chip air and exhausting the compressed air used for driving the air turbine built in the head.
The fluid-passage tube for flowing such fluids therethrough should possess conflicting properties, say, sufficient pressure resistance and flexibility that permits the dental handpiece to yield easily within such a degree that its manipulation properties are not impaired, while preventing its premature deterioration or breaking. Urethane rubber, silicone rubber, vinyl chloride rubber, etc. have been used as the materials to this end with, usually, the thickness thereof of 1 mm or more. The fluid-passage tube is of the structure wherein a detachable, metallic connector is fixed to the end of a connecting pipe extending from the rear end of a grip of the dental handpiece.
Such a conventional dental handpiece is considerably heavy, partly because the fluid-passage tube, metallic connector and handpiece body are weighty in themselves, and partly because the length of the fluid-passage tube connected at its one end with a dental unit body and at its other end with the rear end of the grip thereof through the metallic connector is regulated to about 1.5 m, taking into account the manipulation properties of the handpiece at the time when used by the user such as a dentist, and the fluid paths in the fluid-passage tubes are filled therein with compressed air, cooling water and so on when the handpiece is used. This has been primarily responsible for the problems that while handpiece is used, it is pulled rearward so that the user bears a heavy burden and thus becomes fatigued, and it degrades in manipulation properties.